Consistent Iron Abundances Derived from Neutral and Singly Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-poor Stars
Neutral Fe lines in metal-poor stars yield conflicting abundances depending on whether and how deviations from local thermodynamic equilibrium (LTE) are considered. We have collected new high-resolution and high signal-to-noise ultraviolet (UV) spectra of three warm dwarf stars with [Fe/H] ≈ −2.9 wi...
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| Veröffentlicht in: | The Astrophysical journal 2018-06, Vol.860 (2), p.125 |
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| creator | Roederer, Ian U. Sneden, Christopher Lawler, James E. Sobeck, Jennifer S. Cowan, John J. Boesgaard, Ann Merchant |
| description | Neutral Fe lines in metal-poor stars yield conflicting abundances depending on whether and how deviations from local thermodynamic equilibrium (LTE) are considered. We have collected new high-resolution and high signal-to-noise ultraviolet (UV) spectra of three warm dwarf stars with [Fe/H] ≈ −2.9 with the Space Telescope Imaging Spectrograph on the
Hubble Space Telescope
. We locate archival UV spectra for three other warm dwarfs with [Fe/H] ≈ −3.3, −2.2, and −1.6, supplemented with optical spectra for all six stars. We calculate stellar parameters using methods that are largely independent of the spectra, adopting broadband photometry, color–temperature relations,
Gaia
parallaxes, and assumed masses. We use the LTE line analysis code MOOG to derive Fe abundances from hundreds of Fe
i
and Fe
ii
lines with wavelengths from 2290 to 6430 Å. The [Fe/H] ratios derived separately from Fe
i
and Fe
ii
lines agree in all six stars, with [Fe
ii
/H]–[Fe
i
/H] ranging from +0.00 ± 0.07 to −0.12 ± 0.09 dex, when strong lines and Fe
i
lines with lower excitation potential |
| doi_str_mv | 10.3847/1538-4357/aac6df |
| format | Article |
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Hubble Space Telescope
. We locate archival UV spectra for three other warm dwarfs with [Fe/H] ≈ −3.3, −2.2, and −1.6, supplemented with optical spectra for all six stars. We calculate stellar parameters using methods that are largely independent of the spectra, adopting broadband photometry, color–temperature relations,
Gaia
parallaxes, and assumed masses. We use the LTE line analysis code MOOG to derive Fe abundances from hundreds of Fe
i
and Fe
ii
lines with wavelengths from 2290 to 6430 Å. The [Fe/H] ratios derived separately from Fe
i
and Fe
ii
lines agree in all six stars, with [Fe
ii
/H]–[Fe
i
/H] ranging from +0.00 ± 0.07 to −0.12 ± 0.09 dex, when strong lines and Fe
i
lines with lower excitation potential <1.2 eV are excluded. This constrains the extent of any deviations from LTE that may occur within this parameter range. While our result confirms non-LTE calculations for some warm, metal-poor dwarfs, it may not be generalizable to more metal-poor dwarfs, where deviations from LTE are predicted to be larger. We also investigate trends of systematically lower abundances derived from Fe
i
lines in the Balmer continuum region (≈3100–3700 Å), and we conclude that no proposed explanation for this effect can fully account for the observations presently available.</description><identifier>ISSN: 0004-637X</identifier><identifier>EISSN: 1538-4357</identifier><identifier>DOI: 10.3847/1538-4357/aac6df</identifier><language>eng</language><publisher>Philadelphia: IOP Publishing</publisher><subject>Abundance ; Astrophysics ; Broadband ; Color temperature ; Dwarf stars ; Hubble Space Telescope ; Iron ; Local thermodynamic equilibrium ; Mathematical analysis ; Metallicity ; Metals ; Parameters ; Space telescopes ; Ultraviolet spectra ; Wavelengths</subject><ispartof>The Astrophysical journal, 2018-06, Vol.860 (2), p.125</ispartof><rights>Copyright IOP Publishing Jun 20, 2018</rights><lds50>peer_reviewed</lds50><oa>free_for_read</oa><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-a336t-d832cdf33a43480ee9990ddeda86607ab7c743986ae2a9d47e485660d84aaea93</citedby><cites>FETCH-LOGICAL-a336t-d832cdf33a43480ee9990ddeda86607ab7c743986ae2a9d47e485660d84aaea93</cites><orcidid>0000-0002-8468-9532 ; 0000-0001-5107-8930 ; 0000-0001-5579-9233 ; 0000-0002-3456-5929</orcidid></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><link.rule.ids>314,780,784,27924,27925</link.rule.ids></links><search><creatorcontrib>Roederer, Ian U.</creatorcontrib><creatorcontrib>Sneden, Christopher</creatorcontrib><creatorcontrib>Lawler, James E.</creatorcontrib><creatorcontrib>Sobeck, Jennifer S.</creatorcontrib><creatorcontrib>Cowan, John J.</creatorcontrib><creatorcontrib>Boesgaard, Ann Merchant</creatorcontrib><title>Consistent Iron Abundances Derived from Neutral and Singly Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-poor Stars</title><title>The Astrophysical journal</title><description>Neutral Fe lines in metal-poor stars yield conflicting abundances depending on whether and how deviations from local thermodynamic equilibrium (LTE) are considered. We have collected new high-resolution and high signal-to-noise ultraviolet (UV) spectra of three warm dwarf stars with [Fe/H] ≈ −2.9 with the Space Telescope Imaging Spectrograph on the
Hubble Space Telescope
. We locate archival UV spectra for three other warm dwarfs with [Fe/H] ≈ −3.3, −2.2, and −1.6, supplemented with optical spectra for all six stars. We calculate stellar parameters using methods that are largely independent of the spectra, adopting broadband photometry, color–temperature relations,
Gaia
parallaxes, and assumed masses. We use the LTE line analysis code MOOG to derive Fe abundances from hundreds of Fe
i
and Fe
ii
lines with wavelengths from 2290 to 6430 Å. The [Fe/H] ratios derived separately from Fe
i
and Fe
ii
lines agree in all six stars, with [Fe
ii
/H]–[Fe
i
/H] ranging from +0.00 ± 0.07 to −0.12 ± 0.09 dex, when strong lines and Fe
i
lines with lower excitation potential <1.2 eV are excluded. This constrains the extent of any deviations from LTE that may occur within this parameter range. While our result confirms non-LTE calculations for some warm, metal-poor dwarfs, it may not be generalizable to more metal-poor dwarfs, where deviations from LTE are predicted to be larger. We also investigate trends of systematically lower abundances derived from Fe
i
lines in the Balmer continuum region (≈3100–3700 Å), and we conclude that no proposed explanation for this effect can fully account for the observations presently available.</description><subject>Abundance</subject><subject>Astrophysics</subject><subject>Broadband</subject><subject>Color temperature</subject><subject>Dwarf stars</subject><subject>Hubble Space Telescope</subject><subject>Iron</subject><subject>Local thermodynamic equilibrium</subject><subject>Mathematical analysis</subject><subject>Metallicity</subject><subject>Metals</subject><subject>Parameters</subject><subject>Space telescopes</subject><subject>Ultraviolet spectra</subject><subject>Wavelengths</subject><issn>0004-637X</issn><issn>1538-4357</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2018</creationdate><recordtype>article</recordtype><recordid>eNo9kE1LAzEQhoMoWKt3jwHPq9kmu5scS_0qVD3Uordl3MxKyjZZk7RY_4P_2dSKpzB5n2cGXkLOc3bJpaiu8oLLTPCiugJoSt0ekMH_1yEZMMZEVvLq9ZichLDcjSOlBuR74mwwIaKNdOqdpeO3tdVgGwz0Gr3ZoKatdyv6iOvooaNgNZ0b-95t6dRZ85XyX29mbFKMpYsucRvjOoy_8FMfTZPEeY9NSqhrk_9JX8Cv6ANG6LLeOU_nEXw4JUctdAHP_t4hWdzePE_us9nT3XQynmXAeRkzLfmo0S3nILiQDFEpxbRGDbIsWQVvVVMJrmQJOAKlRYVCFinRUgAgKD4kF_u9vXcfawyxXrq1t-lkPeJlofJC5jJRbE813oXgsa17b1bgt3XO6l3p9a7hetdwvS-d_wDwFXfE</recordid><startdate>20180620</startdate><enddate>20180620</enddate><creator>Roederer, Ian U.</creator><creator>Sneden, Christopher</creator><creator>Lawler, James E.</creator><creator>Sobeck, Jennifer S.</creator><creator>Cowan, John J.</creator><creator>Boesgaard, Ann Merchant</creator><general>IOP Publishing</general><scope>AAYXX</scope><scope>CITATION</scope><scope>7TG</scope><scope>8FD</scope><scope>H8D</scope><scope>KL.</scope><scope>L7M</scope><orcidid>https://orcid.org/0000-0002-8468-9532</orcidid><orcidid>https://orcid.org/0000-0001-5107-8930</orcidid><orcidid>https://orcid.org/0000-0001-5579-9233</orcidid><orcidid>https://orcid.org/0000-0002-3456-5929</orcidid></search><sort><creationdate>20180620</creationdate><title>Consistent Iron Abundances Derived from Neutral and Singly Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-poor Stars</title><author>Roederer, Ian U. ; Sneden, Christopher ; Lawler, James E. ; Sobeck, Jennifer S. ; Cowan, John J. ; Boesgaard, Ann Merchant</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-a336t-d832cdf33a43480ee9990ddeda86607ab7c743986ae2a9d47e485660d84aaea93</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2018</creationdate><topic>Abundance</topic><topic>Astrophysics</topic><topic>Broadband</topic><topic>Color temperature</topic><topic>Dwarf stars</topic><topic>Hubble Space Telescope</topic><topic>Iron</topic><topic>Local thermodynamic equilibrium</topic><topic>Mathematical analysis</topic><topic>Metallicity</topic><topic>Metals</topic><topic>Parameters</topic><topic>Space telescopes</topic><topic>Ultraviolet spectra</topic><topic>Wavelengths</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Roederer, Ian U.</creatorcontrib><creatorcontrib>Sneden, Christopher</creatorcontrib><creatorcontrib>Lawler, James E.</creatorcontrib><creatorcontrib>Sobeck, Jennifer S.</creatorcontrib><creatorcontrib>Cowan, John J.</creatorcontrib><creatorcontrib>Boesgaard, Ann Merchant</creatorcontrib><collection>CrossRef</collection><collection>Meteorological & Geoastrophysical Abstracts</collection><collection>Technology Research Database</collection><collection>Aerospace Database</collection><collection>Meteorological & Geoastrophysical Abstracts - Academic</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>The Astrophysical journal</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Roederer, Ian U.</au><au>Sneden, Christopher</au><au>Lawler, James E.</au><au>Sobeck, Jennifer S.</au><au>Cowan, John J.</au><au>Boesgaard, Ann Merchant</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Consistent Iron Abundances Derived from Neutral and Singly Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-poor Stars</atitle><jtitle>The Astrophysical journal</jtitle><date>2018-06-20</date><risdate>2018</risdate><volume>860</volume><issue>2</issue><spage>125</spage><pages>125-</pages><issn>0004-637X</issn><eissn>1538-4357</eissn><abstract>Neutral Fe lines in metal-poor stars yield conflicting abundances depending on whether and how deviations from local thermodynamic equilibrium (LTE) are considered. We have collected new high-resolution and high signal-to-noise ultraviolet (UV) spectra of three warm dwarf stars with [Fe/H] ≈ −2.9 with the Space Telescope Imaging Spectrograph on the
Hubble Space Telescope
. We locate archival UV spectra for three other warm dwarfs with [Fe/H] ≈ −3.3, −2.2, and −1.6, supplemented with optical spectra for all six stars. We calculate stellar parameters using methods that are largely independent of the spectra, adopting broadband photometry, color–temperature relations,
Gaia
parallaxes, and assumed masses. We use the LTE line analysis code MOOG to derive Fe abundances from hundreds of Fe
i
and Fe
ii
lines with wavelengths from 2290 to 6430 Å. The [Fe/H] ratios derived separately from Fe
i
and Fe
ii
lines agree in all six stars, with [Fe
ii
/H]–[Fe
i
/H] ranging from +0.00 ± 0.07 to −0.12 ± 0.09 dex, when strong lines and Fe
i
lines with lower excitation potential <1.2 eV are excluded. This constrains the extent of any deviations from LTE that may occur within this parameter range. While our result confirms non-LTE calculations for some warm, metal-poor dwarfs, it may not be generalizable to more metal-poor dwarfs, where deviations from LTE are predicted to be larger. We also investigate trends of systematically lower abundances derived from Fe
i
lines in the Balmer continuum region (≈3100–3700 Å), and we conclude that no proposed explanation for this effect can fully account for the observations presently available.</abstract><cop>Philadelphia</cop><pub>IOP Publishing</pub><doi>10.3847/1538-4357/aac6df</doi><orcidid>https://orcid.org/0000-0002-8468-9532</orcidid><orcidid>https://orcid.org/0000-0001-5107-8930</orcidid><orcidid>https://orcid.org/0000-0001-5579-9233</orcidid><orcidid>https://orcid.org/0000-0002-3456-5929</orcidid><oa>free_for_read</oa></addata></record> |
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| subjects | Abundance Astrophysics Broadband Color temperature Dwarf stars Hubble Space Telescope Iron Local thermodynamic equilibrium Mathematical analysis Metallicity Metals Parameters Space telescopes Ultraviolet spectra Wavelengths |
| title | Consistent Iron Abundances Derived from Neutral and Singly Ionized Iron Lines in Ultraviolet and Optical Spectra of Six Warm Metal-poor Stars |
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